Simultaneous grinding machine

ABSTRACT

An apparatus for grinding an elongated workpiece having a plurality of outer surfaces of revolution all centered on a common workpiece axis has a frame and a chuck on the frame for orienting the workpiece with the workpiece axis vertical and for rotating the workpiece about the workpiece axis. Two grinder drive motors on the frame diametrally flank the workpiece axis, are displaceable horizontally and radially of the workpiece axis, and each have a downwardly extending respective vertical drive shaft rotatable about a respective shaft axis, carrying a respective set of at least two vertically and axially spaced grinding wheels, and each having an unsupported and unbraced lower end. The grinders are displaced in respective diametrally opposite horizontal and radial directions for engaging the grinding wheels with the surfaces of the rotating workpiece grinder, such that all the surfaces of the workpiece can be ground simultaneously.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application 13/584/941 filed 14 Aug. 2012 with a claim to the priority of German patent application 10 2011 110 118.0 filed 15 Aug. 2011.

FIELD OF THE INVENTION

The present invention relates to a grinding apparatus. More particularly this invention concerns an apparatus for grinding a plurality of concentric surfaces of a workpiece.

BACKGROUND OF THE INVENTION

A simultaneous grinding apparatus is used on a workpiece having a plurality of coaxial or concentric surfaces of revolution, for instance the journals of a camshaft. The workpiece is rotated about the workpiece axis on which these surfaces are centered and a set of grinding tools is simultaneously urged radially of the workpiece axis, with each such tool engaging a respective one of the surfaces to be ground. The tools are typically grinding wheels also rotatable about a common tool axis parallel to the grinding axis.

As disclosed in US 2012/0164926, it is known to urge a single grinding tool against the workpiece radially opposite the set of grinding wheels. The purpose of this single tool is to grind a surface for engagement by a steady rest. Thus initially the workpiece is ground from both sides, then the tool grinding the steady rest surface is withdrawn and replaced by a steady rest so that the workpiece is held accurately on center for the rest of the grinding operation, allowing the surfaces being engaged on the other side by the grinding wheels to be finish-ground.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved simultaneous grinding machine.

Another object is the provision of such an improved simultaneous grinding machine that overcomes the above-given disadvantages, in particular that can grind all the concentric surfaces of a workpiece in a single operation from coarse to finish grinding.

Another object is to provide a grinding machine whose structure is particularly simple but whose grinding wheel or wheels remain perfectly on center to produce a high-tolerance finished product.

SUMMARY OF THE INVENTION

An apparatus for grinding an elongated workpiece having a plurality of outer surfaces of revolution all centered on a common workpiece axis has according to the invention a frame and means such as a chuck on the frame for orienting the workpiece with the workpiece axis vertical and for rotating the workpiece about the workpiece axis. Two grinder drive motors on the frame diametrally flank the workpiece axis, are displaceable horizontally and radially of the workpiece axis, and each have a downwardly extending respective vertical drive shaft rotatable about a respective shaft axis, carrying a respective set of at least two vertically and axially spaced grinding wheels, and each having an unsupported and unbraced lower end. Means is provided for displacing the grinders in respective diametrally opposite horizontal and radial directions for engaging the grinding wheels with the surfaces of the rotating workpiece grinder, axial spacing and dimensions of the wheels corresponding to axial spacing and dimensions of the surfaces such that all the surfaces of the workpiece can be ground simultaneously.

With this system, the vertically depending shafts only supported and braced at their upper ends can be used for grinding without having to compensate for the weight of the shafts and wheels as in prior-art systems where the shafts are horizontal and must be supported and braced at both ends to remain on center.

In this way most of the radial forces tending to bend or deflect the workpiece are basically canceled out, and it is possible to machine all the surfaces simultaneously with a high degree of precision.

According to the invention each surface of revolution there is at least one respective grinding wheel. More particularly one or two are axially level with one or two of the grinding wheels of the other set so that two of the surfaces are engaged by two grinding wheels. It is also possible for each of the grinding wheels of one of the sets to be axially level with a respective one of the grinding wheels of the other set so that each of the workpiece surfaces is engaged by two grinding wheels. In another arrangement at least one of the grinding wheels of each of the sets is axially between two of the grinding wheels of the other of the sets.

The workpiece according to the invention is a crankshaft and the surfaces include journals between adjacent crankpins and bearing surfaces at ends of the crankshaft, wherein each of the wheels can also engage axially directed faces of flanges carrying the crankpins and flanking the journals. It is not necessary to pre-grind seats for the steady rest.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a small scale partly schematic side elevational view of a simultaneous grinding apparatus according to the invention;

FIGS. 2-5 are detail views of variations on the apparatus of FIG. 1; and

FIG. 6 is a cross-section view of another system according to the invention.

SPECIFIC DESCRIPTION OF THE INVENTION

As seen in FIG. 1 the simultaneous grinding machine or apparatus according to FIG. 1 has a frame 7 on which are mounted a driven headstock 1 and a tailstock 2 for holding and rotating a workpiece 3, here a camshaft with concentric cylindrical journals 12 and bearings 15 and 16, about a vertical axis A. The headstock 1 and tailstock 2 constitute means for holding the workpiece 3 with its axis A axially and radially fixed relative to the frame 7 while rotating the workpiece 3 about the axis A relative to the frame. Two grinders that diametrally flank the axis A are provided for machining the workpiece 3.

The grinders have respective electric drive motors 6 and 6′ mounted on respective horizontal slides 5 and 5′ that can move horizontally in a direction x on respective guide rails 20 and 20′ of respective vertical slides 4 and 4′ in turn mounted on respective vertical guide rails 8 and 8′ for movement in a vertical direction z on the frame 7. Respective motors or actuators 9 and 9′ of the ball/spindle type effect the vertical direction-z movement of the slides 4 and 4′ with the respective motors 6 and 6′ and similar schematically illustrated respective actuators 18 and 18′ serve for shifting the horizontal slides 5 and 5′ in the horizontal direction-x direction on the vertical slides 4 and 4′.

Each grinder motor 6 and 6′ has a respective vertical drive shaft 14 and 14′ that is centered on and rotates about a respective vertical axis 14A and 14A′ and carries a respective set 10 and 10′ of grinding tools 13 and 13′, here standard cylindrical grinding disks or wheels. The shafts 14 and 14′ are seated at their upper ends in the respective motors 6 and 6′ and have unsupported and unbraced lower ends, that is they are in effect cantilever-mounted in the motors 6 and 6′. The wheels 13 and 13′ are axially spaced along and their cylindrical outer surfaces are centered on the respective axes 14A and 14A′ parallel to the vertical direction z and diametrally flanking the axis A. The axial spacings of the tools 13 and 13′ along their respective axes 14 and 14′ correspond to the axial spacing of the bearing surfaces 12, 15 and 16 of the workpiece 3, and the diameters of the wheels 13 and 13′ vary complementarily to the diameters of the surfaces 12, 15 and 16.

According to the invention roughly half of the surfaces 12, 15, and 16 are engaged by the tools 13 and the other half by the tools 13′, and the set 10 of tools 13 is diametrally opposite relative to the axis A of the set 10′ of tools 13′. In this manner the radially inwardly directed forces exerted by the tools 13 and 13′ are roughly equal, with the result that the workpiece 3 remains on center on the axis A with no significant radial deflection caused by the forces applied to it by the grinding operation. The vertical orientation of the shafts 14 and 14′ eliminates the effect of gravity on the axes 14A and 14A′ to ensure the grinding tools 13 and 13′ remain perfectly centered.

FIG. 1 also shows how wheels 13 and 13′ at the ends of the sets 10 and 10′ grind the end bearings 15 and 16, and all of the wheels 13 and 13′ can also serve to machine axially directed side faces of the flanges carrying the crankpins.

There are several manners to further improve the stability of the workpiece 3 according to the invention during machining:

FIG. 2 shows how two tools 13 and 13′ from the sets 10 and 10′ can engage the same journal surface 12, that is a cylindrical surface between two crank pins. Here the surface 12 that is engaged is at or near the axial center of the workpiece 3

FIG. 3 shows an arrangement where two central journals 12 are each engaged by two tools 13 and 13′ as in FIG. 2.

FIG. 4 shows a system where each of the surfaces 12 is engaged by two respective tools 13 and 13′.

FIG. 5 shows a system where the tools 13 and 13′ are axially interleaved, that is at least one tool 13 is between two of the tools 13′ and one of the tools 13′ between two of the tools 13.

Finally FIG. 6 shows a steady rest 17 carried on the frame 7 and urged against the workpiece 3 in a direction perpendicular to a plane defined by the axes A, 14, and 14′. This largely stabilizes the workpiece in a horizontal direction opposite the tangential forces applied to it by the rotating wheels 13 and 13′ turning as indicated by the arrows in opposite directions about the respective axes 14 and 14′. Because of the opposite rotation directions, both wheels 13 and 13′ urge the workpiece 3 in the same tangential direction perpendicular to the plane of the axes A, 14, and 14′ and toward the steady rest 17. This system ensures that the workpiece 3 is very stably centered on the axis A. 

I claim:
 1. An apparatus for grinding an elongated workpiece having a plurality of outer surfaces of revolution all centered on a common workpiece axis, the apparatus comprising: a frame; means on the frame for orienting the workpiece with the workpiece axis vertical and for rotating the workpiece about the workpiece axis; two grinder motors on the frame diametrally flanking the workpiece axis and displaceable horizontally and radially of the workpiece axis and each having a downwardly extending respective vertical drive shaft rotatable about a respective shaft axis, carrying a respective set of at least two vertically and axially spaced grinding wheels, and each having an unsupported and unbraced lower end; and means for displacing the grinders in respective diametrally opposite horizontal and radial directions for engaging the grinding wheels with the surfaces of the rotating workpiece grinder, axial spacing and dimensions of the wheels corresponding to axial spacing and dimensions of the surfaces such that all the surfaces of the workpiece can be ground simultaneously.
 2. The grinding apparatus defined in claim 1, wherein for each surface of revolution there is at least one respective grinding wheel.
 3. The grinding apparatus defined in claim 2, wherein at least one of the grinding wheels of one of the sets is axially and vertically level with one of the grinding wheels of the other set so that the respective surface is engaged by two grinding wheels.
 4. The grinding apparatus defined in claim 2, wherein two of the grinding wheels of one of the sets are axially level and vertically with two of the grinding wheels of the other set so that two of the surfaces are engaged by two grinding wheels.
 5. The grinding apparatus defined in claim 2, wherein each of the grinding wheels of one of the sets is axially level with a respective one of the grinding wheels of the other set so that each of the workpiece surfaces is engaged by two grinding wheels.
 6. The grinding apparatus defined in claim 2, wherein at least one of the grinding wheels of each of the sets is axially between two of the grinding wheels of the other of the sets.
 7. The grinding apparatus defined in claim 1, wherein the workpiece is a crankshaft and the surfaces include journals between adjacent crankpins and bearing surfaces at ends of the crankshaft, each of the wheels also being engageable with axially directed faces of flanges carrying the crankpins and flanking the journals.
 8. The grinding apparatus defined in claim 1, further comprising: a steady rest engageable with the workpiece in a direction perpendicular to a plane defined by the workpiece axis and shaft axes about which the wheels are rotated.
 9. An apparatus for grinding an elongated workpiece having a plurality of outer surfaces of revolution all centered on a common workpiece axis, the apparatus comprising: a frame; means on the frame for orienting the workpiece with the workpiece axis vertical and for rotating the workpiece about the workpiece axis; two grinder drives on the frame diametrally flanking the workpiece axis and displaceable radially of the workpiece axis and each having a respective vertically depending shaft carrying a respective set of at least two axially spaced grinding wheels, a lower end of each shaft being unsupported and unbraced; means for displacing the grinders in respective diametrally opposite horizontal directions for horizontally engaging the grinding wheels with the surfaces of the rotating workpiece grinder, axial spacing and dimensions of the wheels corresponding to axial spacing and dimensions of the surfaces such that all the surfaces of the workpiece can be ground simultaneously; and a steady rest engageable horizontally with the workpiece in a direction perpendicular to a plane defined by the workpiece axis and axes about which the wheels are rotated and opposite a direction in which rotation of the wheel urges the workpieces.
 10. The grinding apparatus defined in claim 9, wherein the sets are rotated about respective axes diametrally flanking the workpiece axis in such a direction as to exert tangential forces on the workpiece urging the workpiece against the steady rest. 